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What is fatigue?

Fatigue is a physiological condition that can occur long before you fall asleep at the wheel. It has a negative impact on your reaction time, your ability to concentrate and your general understanding of the road and traffic around you. The three main causes of fatigue are as follows.

  • Sleep loss — this is the most commonly-known cause of fatigue. Different individuals require different levels of sleep, although the average is 7 to 8 hours of sleep a day. If you do not get a full night’s sleep, it is likely to cause fatigue and this can build up over time if your sleep continues to be restricted.
  • Circadian rhythms — everybody has a built-in body clock in the brain that biologically determines when they will feel sleepy. These circadian rhythms programme us to feel at our most sleepy between 3am and 5am, and between 3pm and 5pm.
  • Time spent driving/working — research shows that the longer people spend driving without a break, the greater their level of fatigue. Also, the time spent in other activities such as work, school, and so on, can increase fatigue and affect subsequent driving.

Research shows that fatigue is difficult to identify and recognise as having a role in a crash (Williamson and Chamberlain, 2005), so the contribution of fatigue to crashes may be under-represented in the police-reported crash system that has been used for this fact sheet.

Note:  For additional information on the causes of fatigue and how to prevent them see the NZ Transport Agency Fatigue fact sheet here www.nzta.govt.nz/safety/driving-safely/fatigue/, and the National Highway Traffic Safety Administration (NHTSA - United States Department of Transport) fact sheet here www.nhtsa.gov/risky-driving/drowsy-driving

Next: Fatigue crashes and casualties